Method of manufacturing an SOI (silicon on insulator ) wafer

ABSTRACT

This invention is to manufacturing of SOI (Silicon On Insulator) wafer; with respect to manufacturing of SOI wafer, preparation process of silicon wafer with desired thickness ( 100 ), deposition of Alumina(Al 2 O 3 ) as insulator by an ALE (Atomic Layer Epitaxial) method such as ALCVD, ALD, ASCVD, etc . . . ( 110 ), bonding of this wafer with another silicon wafer by various bonding methods ( 120 ), Cutting of this bonded wafer by various methods of cutting( 130 ), Polishing the surface of the cut wafer ( 140 ). For the insulator material, titanium oxide (TiO 2 ) or tantalum oxide(Ta 2 O 5 ) can be used other than Alumina(Al 2 O 3 ) and such bonding process can be done by unibonding method and cutting method can be done by Smart Cut process.

BACKGROUND OF THE INVENTION

[0001] This invention is to suggest a different method of manufacturingSOI wafer and more specifically, to improve chemical, mechanical , andelectrical properties of SOI wafer, to diversify the structure andcomposition of the wafer, and to improve on fabrication process of suchwafers.

[0002] Silicon On Insulator type of wafers is widely used in wafermanufacturing process. This process is to form an insulator on top ofthe semiconductor wafer and then to form single crystal silicon layerbefore fabrication of semiconductor device.

[0003] SOI wafer is known to offer lateral and vertical isolation ofintegrated components and also to provide devices with superiorelectrical properties.

[0004] In a SOI wafer, two different processes are widely used ingeneral. One of them is so called BE (Bond and Etch) method, which is tobond two wafers and etch back one of them in order to make a thin layer.The other is called SIMOX(Separation By Implantation of oxygen) method,which is to implant oxygen deep into the silicon wafer and form a buriedoxide and a thin silicon layer by post-implantation heat treatment.

[0005] Smart Cut process is to implant hydrogen ions into an oxidizedwafer A (through the insulator) by controlling the energy (depth) ofhydrogen ions in order to control the film thickness. This wafer A isthen bonded to another silicon wafer B. During subsequent annealing,bonded wafers separate at the region where the implanted hydrogen ionshave stopped. This separation results in a thin Si film separated fromthe wafer B by a buried oxide. Finally, CMP process is applied in orderto obtain a smoother surface and the desired thickness of the siliconfilm. This method is relatively easier than other processes such asSIMOX method and therefore, is being widely used recently.

[0006] In the Smart Cut technology mentioned above, the Smart Cutprocess disclosed in U.S. Pat. No. 5,882,987 (Smart Cut process withthin film semiconductor material on insulating film) claims to use CMPprocess in order to solve non-uniform surface problem and thin filmformation problem, which are known problems associated with Smart Cutprocesses.

[0007] In case where SiO₂ is used as an insulation film, the thicknessand quality of the buried insulator is controlled with conventionaltechnologies (oxidation). Since the chemical properties change byheating above 1000° C. in dry oxygen ambient(see table 4), such acontrol is not perfect.

SUMMARY OF THE INVENTION

[0008] The invention is to generate SOI wafer despite all the knownproblems associated with it. It is the purpose of this invention toimprove the film properties, to generate uniform surface structurewithout requiring high process temperature, and to diversify the natureof the insulating film. This new invention of SOI wafer manufacturingmethod includes steps of: (100) Preparation of silicon wafers withdesigned thickness and diameter; (110) forming alumina (Al₂O₃)insulation film or other dielectric film on the surface of the preparedsilicon wafer by atomic layer epitaxial method such as ALCVD, ALD,ASCVD, etc.; (120) Bonding this wafer with another silicon wafer(oxidized or not) by various methods; (130) Cutting one of the bondedwafers by various methods; (140) Polishing the cut surface of the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] These and other features, aspects and advantages of the presentinvention will become better understood with reference to theaccompanying drawings, wherein:

[0010]FIG. 1 indicates a partial side view of the wafer, showingsequential manufacturing process of the invention;

[0011]FIG. 2 indicates a partial side view of the wafer, done by the SOIwafer manufacturing process of the invention;

[0012]FIG. 3 indicates the process flowchart explaining the SOI wafermanufacturing process of the invention ; and

[0013]FIG. 4 represents conventional SiO₂ film generating method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] The basic concept of the system configuration and methods ofmanufacturing are explained more in detail by the drawings. FIG. 1indicates a partial side view of the wafer, showing sequentialmanufacturing process of the invention; FIG. 2 indicates a partial sideview of the wafer, done by the SOI wafer manufacturing process of theinvention; FIG. 3 indicates the process flowchart explaining the SOIwafer manufacturing process of the invention; and FIG. 4 representsconventional SiO₂ film generating method.

[0015] The characteristic of this invention is that various methods areused for bonding and cutting wafers in order to achieve SOI-likestructures using dielectric films such as alumina (Al₂O₃), TitaniumOxide (TiO₂), tantalum oxide (Ta₂O₅), etc . These films are easy tofabricate by ALCVD and have more applications than conventional SiO₂films in subsequent circuit integration processes. According to thisinvention, besides the conventional Smart Cut processes, other methodscan be used such as BE(Bond & Etch) and Eltran (Separation By usingPorous Silicon). This invention uses alumina instead of SiO₂ and alsoutilizes atomic layer epitaxial method instead of conventional CVDprocess or oxygen implantation. Alumina is a lot easier to make thinfilms since it is more ductile and has greater conductivity than SiO₂.Furthermore, it's more corrosion-resistant due to its superior chemicalreactivity than with SiO₂. Other key advantages are the better thermalconductivity and increased dielectric constant.

[0016] Other insulating materials suggested in this invention aretitanium oxide(TiO₂), tantalum oxide(Ta₂O₅), hafnium oxide, etc. Theircharacteristics are known to be either similar or better than that ofalumina(Al₂O₃). One method of Atomic Layer Epitaxial (ALE) is a processwhere films are generated by stack of atomic layers using chemicalabsorption and desorption. ALE is preferred since it is by using surfacesaturated reaction to deposit the desired material by sequentialdeposition in order to produce very thin film thus able to achieveprecise control of film thickness. The main difference as compared toconventional silicon-on-sapphire material is that instead of growing Sion Sapphire (which generates many defects), in this invention alumina isgrown on silicon.

[0017] By using the proposed method in this invention, it is possible togenerate alumina films at below 700° C. which is significantly lowerthan 1000° C. required for SiO©ü film, with 1000 times less currentleakage rate than that of SiO₂ film. Furthermore, the life of the filmis increased due to corrosion-resistant characteristics of alumina film,and it is also possible to very the film characteristics by varying thefilm thickness due to precise control of atomic layers.

[0018] The following is a detailed description of the exemplaryembodiment and only is an example of this invention. Other ideas andpurpose can be derived from this invention and such derivatives are allincluded within the technical aspect of this invention.

[0019] [Embodiment]

[0020] Process 1:

[0021] (100)Prepare a silicon wafer with desired thickness/diameter

[0022] Process 2:

[0023] (110)Generate alumina film (or other dielectric) as an insulatoron top of the wafer via ALE process such as ALCVD, ALD, ASCVD, etc.

[0024] Process 3:

[0025] (120)Bonding the wafer with alumina insulator and silicon wafer(oxidized or not) via unibonding or other bonding method

[0026] Process 4:

[0027] (130)Cut one of the bonded wafers via Smart Cut method or othercutting method

[0028] Process 5

[0029] (140)Polish the cut surface of the bonded wafers to make itsmooth This new method of manufacturing SOI water is by using alumiana,titanium oxide, tantalum oxide or other oxides instead of SiO₂ asinsulato. The new SOI wafers will be fabricated with less than ⅔ of theheat required for SiO₂ process. By doing so, it is possible to achieveboth achieve both cost reduction and superior characteristics of the Sifilm and buried dielectric (high thermal conductivity and dielectricconstant, good quality Si-Al203 interface, etc)

[0030] In this new manufacturing method, leakage current can be reducedmore than 1000 times, as compared to SiO₂, thus achieving significantimprovement in electrical properties and flexibility.

[0031] In addition, improvement in design application and longerlifetime can be achieved by utilizing the ability of the ALCVD processto control atomic scale level and high breakdown voltage.

[0032] It will be apparent to those skilled in the art that variouscontrols and variations can be made in the present invention withoutdeviating from the spirit or scope of the invention. Thus, it isintended that the present invention covers the controls and variationsof this invention provided they come within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A method of manufacturing an SOI(Silicon OnInsulator) wafer, comprising the steps of: preparing a silicon waferwith designed thickness and diameter; forming alumina(Al₂O₃) or otherdielectric as an insulator layer on the surface of the prepared siliconwafer by ALE process such as ALCVD, ALD, ASCVD, etc.; bonding the waferwith another silicon wafer by various method of bonding; cutting thebonded wafers by various method; and polishing the surface of the cutwafer
 2. The method of claim 1, wherein subject of said insulator layercan be titanium oxide(TiO₂)and tantalum oxide (Ta₂O₅) instead of alumina(Al₂O₃)
 3. The method of claim 1, wherein said bonding process may be aunibonding method
 4. The method of claim 1, wherein said cutting processmay be a Smart Cut method